There is no scarier book in the world than The Exorcist, celebrating its 40th anniversary this year with a new edition. When I first read this book, it frightened me so much that I have still not seen the movie to this day. The book gave me enough awful images for a lifetime...I didn't need to see it on the screen too.
Author William Blatty has revamped his infamous storyline, adding new characters and passages. But the core remains the same: Young Regan begins to hear voices and suffer from nightmares after her parents' divorce, which seems at first to be related to the stress of the change. She claims, and others begin to believe, that she is possessed by the devil himself.
Blatty says this new edition is the version he always wanted to write, and the one he wants to be remembered for. He says he never really set out to terrify anyone, but really saw the book as a supernatural detective story. See his interview on the 40th anniversary book by clicking here. (Reissue in 2011 - Harper)